Minactivin (PAI-2) is a naturally occurring inactivator of urokinase-type plasminogen activators. This type of plasminogen activator is found in abnormally high levels in many major human carcinomas, most notably lung, colon, breast and prostate. Plasminogen activators are serine proteases which are thought to mediate the proteolytic cascade involved in cellular translocation, migration and invasion. As such, they appear to be associated with tissue destruction and remodelling, and have been implicated in tumor growth and metastasis. They may also have a role in inflammatory reactions.
Plasminogen activators are generally found to be of two types: 1) urokinase--type and 2) tissue--type. Tissue-type plasminogen activator is mainly found in the blood and blood vessel walls and where it is responsible for activating the fibrinolytic defence system against thrombosis. Urokinase-type plasminogen activators do not appear to play a role in normal thrombolytic processes but have been implicated in those pathological events associated with invasion and tissue destruction, in particular, tumor metastasis and inflammatory reactions.
Several inhibitors specific for plasminogen activators have been described with include one isolated from placenta (Holmberg, L. Biochim. Biophys. Acta 544, 128-137 (1978) and another (PAI-1) which is produced in cultured vascular endothelial cells (Van Mourik, J. A. Lawrence, D. A., Loskutoff, D. J., J. Biol. Chem., 259, 14914-14921 (1984)). Minactivin was found to be produced by blood monocytes and U937 cells and appears to be immunologically related to the placental inhibitor. The relationship between these various inhibitors is presently unknown.
As is the case with most other potent biologically active proteins, minactivin is produced in very small amounts in vivo, and as such, is difficult to purify and characterise by conventional biochemical approaches. Therefore,as large quantities of purified minactivin are required for further evaluation of its properties and biological efficacy in clinical applications, it is desirable to produce the protein using recombinant DNA techniques; that is, by cloning the minactivin gene into an alternate host, such as bacteria or animal cells. In order to clone minactivin it is desirable to purify to homogeneity the small amounts that can be so purified of naturally occurring minactivin in order to produce antibodies, amino acid sequences, peptide fragments and synthetic oligonucleotides derived from said purified minactivin. These reagents are of use in cloning strategies.